Biology subjects

Parikh, B. A.

Publications and source records attributed to Parikh, B. A..

4 recordsLinked to original sources

bioRxiv2024

Expression of a single inhibitory Ly49 receptor is sufficient to license NK cells for effector functions

Natural killer (NK) cells recognize target cells through germline-encoded activation and inhibitory receptors enabling effective immunity against viruses and cancer. The Ly49 receptor family in the mouse and killer immunoglobin-like receptor family in humans play a central role in NK cell immunity through recognition of MHC class I and related molecules. Functionally, these receptor families are involved in licensing and rejection of MHC-I-deficient cells through missing-self. The Ly49 family is highly polymorphic, making it challenging to detail the contributions of individual Ly49 receptors to NK cell function. Herein, we showed mice lacking expression of all Ly49s were unable to reject missing-self target cells in vivo, were defective in NK cell licensing, and displayed lower KLRG1 on the surface of NK cells. Expression of Ly49A alone on a H-2Dd background restored missing-self target cell rejection, NK cell licensing, and NK cell KLRG1 expression. Thus, a single inhibitory Ly49 receptor is sufficient to license NK cells and mediate missing-self in vivo.

immunology↗

bioRxiv2023

The highly conserved stem-loop II motif is dispensable for SARS-CoV-2

The stem-loop II motif (s2m) is a RNA structural element that is found in the 3 untranslated region (UTR) of many RNA viruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Though the motif was discovered over twenty-five years ago, its functional significance is unknown. In order to understand the importance of s2m, we created viruses with deletions or mutations of the s2m by reverse genetics and also evaluated a clinical isolate harboring a unique s2m deletion. Deletion or mutation of the s2m had no effect on growth in vitro, or growth and viral fitness in Syrian hamsters in vivo. We also compared the secondary structure of the 3 UTR of wild type and s2m deletion viruses using SHAPE-MaP and DMS-MaPseq. These experiments demonstrate that the s2m forms an independent structure and that its deletion does not alter the overall remaining 3UTR RNA structure. Together, these findings suggest that s2m is dispensable for SARS-CoV-2. IMPORTANCERNA viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contain functional structures to support virus replication, translation and evasion of the host antiviral immune response. The 3 untranslated region of early isolates of SARS-CoV-2 contained a stem-loop II motif (s2m), which is a RNA structural element that is found in many RNA viruses. This motif was discovered over twenty-five years ago, but its functional significance is unknown. We created SARS-CoV-2 with deletions or mutations of the s2m and determined the effect of these changes on viral growth in tissue culture and in rodent models of infection. Deletion or mutation of the s2m element had no effect on growth in vitro, or growth and viral fitness in Syrian hamsters in vivo. We also observed no impact of the deletion on other known RNA structures in the same region of the genome. These experiments demonstrate that the s2m is dispensable for SARS-CoV-2.

microbiology↗

bioRxiv2022

The highly conserved stem-loop II motif is important for the lifecycle of astroviruses but dispensable for SARS-CoV-2

The stem-loop II motif (s2m) is an RNA element present in viruses from divergent viral families, including astroviruses and coronaviruses, but its functional significance is unknown. We created deletions or substitutions of the s2m in astrovirus VA1 (VA1), classic human astrovirus 1 (HAstV1) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For VA1, recombinant virus could not be rescued upon partial deletion of the s2m or substitutions of G-C base pairs. Compensatory substitutions that restored the G-C base-pair enabled recovery of VA1. For HAstV1, a partial deletion of the s2m resulted in decreased viral titers compared to wild-type virus, and reduced activity in a replicon system. In contrast, deletion or mutation of the SARS-CoV-2 s2m had no effect on the ability to rescue the virus, growth in vitro, or growth in Syrian hamsters. Our study demonstrates the importance of the s2m is virus-dependent.

microbiology↗

bioRxiv2019

Major histocompatibility complex class I-restricted protection against murine cytomegalovirus requires missing-self recognition by the natural killer cell inhibitory Ly49 receptors

Viruses have evolved strategies that highlight critical, intertwined host immune mechanisms. As postulated by the missing-self hypothesis, natural killer (NK) cells and major histocompatibility complex class I (MHC-I)-restricted cytotoxic T lymphocytes (CTLs) have opposing requirements for ubiquitously expressed MHC-I molecules. Since NK cell MHC-I-specific Ly49 inhibitory receptors prevent killing of cells with normal MHC-I, viruses evading CTLs by down-regulating MHC-I should be vulnerable to NK cells. However, definitive integrated in vivo evidence for this interplay has been lacking, in part due to receptor polymorphism and a proposed second function of Ly49 receptors in licensing NK cells via self-MHC-I. Here we generated mice lacking specific Ly49 inhibitory receptors to show their essential role in licensing and controlling murine cytomegalovirus (MCMV) infection in vivo in an MHC-restricted manner. When MCMV cannot down-regulate MHC-I, NK cells cannot control infection that instead is mediated by CTLs, as predicted by the missing-self hypothesis.

immunology↗